A method has been developed which identifies a class of genes relatively important in neoplasia-predisposition in the general population and which measures the risk of malignant neoplasms for heterozygous carriers of each gene in this class. This method is based on autosomal recessive syndromes associated with cancer and leukemia. The heterozygous carriers of genes for each of these syndromes occur in the population at a frequency between 0.01 and 0.001, so that detecting a significant increase in risk of a malignant neoplasm for the heterozygous carrier of any of these genes would imply that gene is an important neoplasia-predisposing gene of man. An association between malignant neoplasms and each gene in this class can be detected by a retrospective study of the illnesses and causes of death in families with homozygous probands (affected with a particular autosomal recessive syndrome), since heterozygotes are frequent in such families. Finding such associations may provide useful leads for further investigations of oncogenesis in man. Genes predisposing to diabetes mellitus or other serious illnesses may be detected and analyzed by the same methods of data collection and analysis.